Determining Individual Particle Magnetizations in Assemblages of Micrograins. Issue 7 (6th April 2018)

• Record Type: Journal Article
• Authors: de Groot, Lennart V.; Fabian, Karl; Béguin, Annemarieke; Reith, Pim; Barnhoorn, Auke; Hilgenkamp, Hans
• Is Part Of: Geophysical research letters. Volume 45:Issue 7(2018)
• Page Start: 2995
• Page End: 3000
• Publication Date: 2018-04-06
• Subjects: rock magnetism -- rock physics; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL076634
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Obtaining reliable information from even the most challenging paleomagnetic recorders, such as the oldest igneous rocks and meteorites, is paramount to open new windows into Earth's history. Currently, such information is acquired by simultaneously sensing millions of particles in small samples or single crystals using superconducting quantum interference device magnetometers. The obtained rock‐magnetic signal is a statistical ensemble of grains potentially differing in reliability as paleomagnetic recorder due to variations in physical dimensions, chemistry, and magnetic behavior. Here we go beyond bulk magnetic measurements and combine computed tomography and scanning magnetometry to uniquely invert for the magnetic moments of individual grains. This enables us to select and consider contributions of subsets of grains as a function of particle‐specific selection criteria and avoid contributions that arise from particles that are altered or contain unreliable magnetic carriers. This new, nondestructive, method unlocks information from complex paleomagnetic recorders that until now goes obscured. Plain Language Summary: Information about the past state of the Earth's magnetic field is obtained from igneous rocks that take a snapshot of the ambient magnetic field as they cool. Igneous rocks, however, contain a broad range of different grains that have their specific magnetic properties, and many are known to be incapable of storing a magnetization reliably over time. The signal obtained from traditional bulk samples that contain many millions of grains is a statistical ensemble of all these grains—the good and the bad. To improve the quality of the magnetic signal from these rocks, we go beyond bulk samples and identify magnetizations of individual grains in a sample using an X‐ray tomography‐assisted magnetic inversion. We show that it is possible to uniquely and nondestructively obtain magnetizations for a limited number of grains. Isolating the individual magnetizations of grains enables selecting only the known good recorders and rejecting the adverse recorders present in the sample. This would make it possible to obtain information from even the most complex paleomagnetic recorders, including igneous rocks, meteorites, and extraterrestrial material that until now goes obscured. Key Points: Individual magnetic moments are isolated for a suite of grains while embedded in a nonmagnetic medium using micromagnetic tomography The traditional nonuniqueness of this inversion problem is tackled by adding spatial information using microCT scanning Our new technique is nondestructive; hence, grains can be analyzed multiple times and in different magnetic states